Re: [PATCH] fork: fail on non-zero higher 32 bits of args.exit_signal

[Christian Brauner <christian.brauner@ubuntu.com>]

On Tue, Sep 10, 2019 at 03:09:35PM +0200, Christian Brauner wrote:
> On Tue, Sep 10, 2019 at 02:44:41PM +0200, Oleg Nesterov wrote:
> > On 09/10, Eugene Syromiatnikov wrote:
> > >
> > > --- a/kernel/fork.c
> > > +++ b/kernel/fork.c
> > > @@ -2562,6 +2562,9 @@ noinline static int copy_clone_args_from_user(struct kernel_clone_args *kargs,
> > >  	if (copy_from_user(&args, uargs, size))
> > >  		return -EFAULT;
> > >  
> > > +	if (unlikely(((unsigned int)args.exit_signal) != args.exit_signal))
> > > +		return -EINVAL;
> > 
> > Hmm. Unless I am totally confused you found a serious bug...
> > 
> > Without CLONE_THREAD/CLONE_PARENT copy_process() blindly does
> > 
> > 	p->exit_signal = args->exit_signal;
> > 
> > the valid_signal(sig) check in do_notify_parent() mostly saves us, but we
> > must not allow child->exit_signal < 0, if nothing else this breaks
> > thread_group_leader().
> > 
> > And afaics this patch doesn't fix this? I think we need the valid_signal()
> > check...
> 
> Thanks for sending this patch so quickly after our conversation
> yesterday, Eugene!
> We definitely want valid_signal() to verify the signal is ok.
> 
> Eugene, can you please update the patch to use valid signal and keep it
> as a separate patch from the cleanup and selftest patches?

I'll then pick this up quickly so we can get this in before 5.3 is out.

Thanks!
Christian